1. Field of the Invention
This invention relates to improvements in a radiography apparatus which is provided with a gas chamber for enveloping therein gas ionizable by an ionizing radiation such as X-rays or .gamma.-rays and forms an electrostatic image of a body to be examined.
2. Description of the Prior Art
Radiography apparatus provided with a gas chamber for enveloping therein ionizing gas is known from, for example, published German Pat. No. 1,497,093 specification (hereinafter referred to as DAS No. 1,497,093) or open German Pat. No. 2,258,364 specification (hereinafter referred to DOS No. 2,258,364). The apparatus disclosed in DOS No. 2,258,368 is provided with a high pressure gas chamber. In the high pressure gas chamber, an anode and a cathode to which is applied a DC voltage are disposed in a predteremined spaced-apart relationship. Ionizing gas, for example, a mixture of xenon and a small amount of quenching gas is enveloped in the gas chamber at a pressure above the atmospheric level. An insulating film is disposed on the anode in opposed relationship with the cathode. The radiation passed through a body to be examined ionizes the gas in the chamber. By the action of the electric field, positive ions are acceleratedly attracted toward the cathode while electrons are acceleratedly attracted toward the cathode while electrons are acceleratedly attracted toward the anode, thereby further producing a number of secondary electrons. As a result, these electrons are deposited onto the insulating film on the anode, thus forming an image pattern. In this manner, an electrostatic latent image of the body to be examined is formed. The apparatus disclosed in DAS No. 1,497,093 is substantially similar in construction to that disclosed in DOS No. 2,258,364, excepting that the gas in the gas chamber is at a low pressure and that electrons are bombarded from a heavy metal such as lead or the like.
In these apparatuses of the prior art, the electrostatic latent image formed in taken out of the gas chamber and developed by the use of common electrophotographic developing method. By that time, the ionizing gas filling the gas chamber has already been discharged. Likewise, the gas chamber is evacuated when the film is placed thereinto.
In this way, gas is supplied to and discharged from the gas chamber at every picture-taking cycle, so that operation of the apparatus is cumbersome and difficult and accordingly limited in rapid continuous picture-taking. Further, removal of the film with the gas chamber open results in leakage, and accordingly loss, of the gas and in some cases, the leaked gas may adversely affect the human bodies or the like, and in addition, such loss of the gas would be particularly expensive if the gas were xenon or the like.